I couldn't find any valid information on what causes impostor syndrome. Are there any studies of it?
Castro, Jones, and Mirsalimi (2004) examine the relation between parentification and impostor syndrome, but they also give a good overview of other literature on the subject. They enumerate a number of traits (low global self-esteem, introversion, neuroticism, perfectionism, and attributing success to external factors) and psychological problems (anxiety, depression, psychological distress, and generally poor mental health) that are associated with impostor syndrome, but when you refer to "causes", I assume you are most interested in childhood issues associated with the syndrome.
As mentioned, parentification (the child taking on emotional or other responsibilities that normally rest on the parent) has been researched as a risk factor for developing impostor syndrome; they were found found to be moderately correlated. In addition to this, King & Cooley (1995) found that a family culture that places a high value on achievement is associated with impostor syndrome. Sonnak and Towell (2001) found that having overprotective and/or controlling parents, and having low self esteem are the two best predictors for impostor syndrome, accounting for half the variation in feelings of being an impostor.
- Castro, D. M., Jones, R. A., Mirsalimi, H. (2004). Parentification and the Impostor Phenomenon: An Empirical Investigation. The American Journal of Family Therapy, 32, 205-216.
- King, J. E., Cooley, E. L. (1995). Achievement Orientation and the Impostor Phenomenon among College Students. Contemporary Educational Psychology, 20(3), 304-312.
- Sonnak, C., Towell, T. (2001). The impostor phenomenon in British university students: Relationships between self-esteem, mental health, parental rearing style and socioeconomic status. Personality and Individual Differences, 31(6), 863-874.